Joint transmitter signal processing in multi-beam satellite systems

Abstract

A, method and apparatus for wirelessly transmitting data to a plurality of terminals in each of a plurality of beams through a plurality of transmit feeds includes selecting, for each beam, two or more terminals among the plurality of terminals in the beam as a subgroup of terminals, on the basis of channel state information of the plurality of terminals; determining, for each beam, equivalent channel state information representing the subgroup of terminals in the beam on the basis of the channel state information of the terminals of at least one of the plural subgroups of terminals; and determining a set of weight coefficients that relate the plurality of transmit feeds to a plurality of signals that are intended for transmission in the plurality of beams on the basis of the equivalent channel state information representing the plural subgroups of terminals. Also disclosed is a method and apparatus for receiving data transmitted via wireless transmission to a plurality of beams through a plurality of transmit feeds and estimating a channel on the basis of the received data. The present disclosure is advantageously applicable to satellite communication systems.

What is claimed is: 
     
       1. A method for channel estimation in a wireless MU-MIMO communication system employing preceding, the method comprising steps of:
 (A) receiving a signal comprising a plurality of waveform components, each waveform component being subdivided into frame units, wherein each frame unit has a first field that is not subjected to precoding and that indicates a start of the respective frame unit and one or more second fields that are not subjected to the precoding and that each comprise a pilot sequence; 
 (B) for a waveform component of the plurality of waveform components, determining a start of a frame unit of the waveform component by searching in the received signal for the first field indicating the start of the frame unit; 
 (C) determining a time offset of the waveform component by referring to the first field in the frame unit and the one or more second fields in the frame unit; 
 (D) re-sampling the waveform component on the basis of the determined time offset to obtain a re-sampled waveform component; 
 (E) determining a frequency offset and a phase offset of the re-sampled waveform component by referring to the one or more second fields in the frame unit of the resampled waveform component; and 
 (F) estimating a channel coefficient corresponding to the waveform component by referring to the one or more second fields in the frame unit, on the basis of the determined frequency offset and phase offset of the re-sampled waveform component, 
 wherein the above steps are performed in the order (A) to (F). 
 
     
     
       2. The method according to  claim 1 , wherein steps (B) to (F) are performed for each of the plurality of waveform components. 
     
     
       3. The method according to  claim 1 , further comprising the steps of:
 (G) generating a replicated frame unit comprising replica of the first field and the one or more second fields of the frame unit of the waveform component on the basis of the determined time offset, frequency offset, phase offset and channel coefficient; and 
 (H) subtracting the replicated frame unit from the received signal, 
 wherein steps (G) and (H) are performed after step (F); and 
 the method further comprises performing steps (A) to (F) again for another waveform component of the received signal after performing step (H). 
 
     
     
       4. The method according to  claim 3 , wherein steps (B) to (H) are performed for each of the plurality of waveform components. 
     
     
       5. The method according to  claim 3 , further comprising the steps of:
 (I) estimating a frequency of the received signal; 
 (J) determining a matched filter on the basis of the estimated frequency and filtering the received signal using the determined matched filter; and 
 (K) de-multiplexing the waveform component to separate the first field and the one or more second fields in the frame unit of the waveform component, 
 wherein steps (G) and (H) are performed after step (A) and before step (B), and step (K) is performed after step (B) and before step (C). 
 
     
     
       6. An apparatus for estimating a channel in a wireless MU-MIMO communication system employing precoding, the apparatus comprising:
 a reception unit configured for receiving a signal comprising a plurality of waveform components, each waveform component being subdivided into frame units, wherein each frame unit has a first field that is not subjected to precoding and that indicates a start of the respective frame unit and one or more second fields that are not subjected to the precoding and that each comprise a pilot sequence; 
 a frame synchronization unit configured for determining a start of a frame unit of a waveform component of the plurality of waveform components by searching in the received signal for the first field indicating the start of the frame unit; 
 a time offset determination unit configured for determining a time offset of the waveform component by referring to the first field in the frame unit and the one or more second fields in the frame unit; 
 a re-sampling unit configured for re-sampling the waveform component on the basis of the determined time offset to obtain a re-sampled waveform component; 
 a frequency/phase offset determination unit configured for determining a frequency offset and a phase offset of the re-sampled waveform component by referring to the one or more second fields in the frame unit of the re-sampled waveform component; and 
 a channel coefficient estimation unit configured for estimating the channel coefficient corresponding to the waveform component by referring to the one or more second fields in the frame unit, on the basis of the determined frequency offset and phase offset of the re-sampled waveform component.